Yesterday my son asked for help to open dds files in Photoshop. After some googling, I found this NVIDIA plugin for Photoshop and some articles, which complained that it does not work with Photoshop CS4 64bit. To solve this problem it was necessary to understand two things: that when 64bit version of Photoshop was installed, 32bit version also was installed, and that NVIDIA DDS plugin put the dds.8bi file to C:\Program Files\Adobe\Adobe Photoshop CS4 (64 Bit)\Plug-ins\File Formats folder.

So, to open dds files in Photoshop:

1. download and install this NVIDIA plugin for Photoshop;
2. copy dds.8bi file from C:\Program Files\Adobe\Adobe Photoshop CS4 (64 Bit)\Plug-ins\File Formats folder to C:\Program Files (x86)\Adobe\Adobe Photoshop CS4\Plug-ins\File Formats folder;
3. run 32bit Photoshop version from C:\Program Files (x86)\Adobe\Adobe Photoshop CS4\

Hope this helps someone.